Point actuation and layout design

Part 2 Motorised point machines

Last month, the features of solenoid and manual turnout control were investigated, along with their suitability for certain layout types. Stall and switched motors are next in our two-part comparison of point motor types.

MAKING the right choices for turnout control is one of the more important decisions a modeller can make when embarking on a new layout project. Hopefully, the layout will become an enjoyable project (they are never finished after all) which will be reliable and fun to operate.

Selecting the right components, including point motors (machines) at the start, will do much for reliability and subsequent satisfaction with the hobby.

Layout planning

It is at the layout planning stage that point motor types and size should be carefully considered.

For example, a stall motor such as the Circuitron ‘Tortoise’ has a large mounting footprint and might be hard to fit in any number where there are complex junctions, something ‘N’ gauge modellers have to consider. Baseboard framing has to be planned in conjunction with track design, with the precise position of turnouts carefully located so they do not cross baseboard members at the points. Otherwise, how are you going to mount the motor underneath the points?

Fixing holes in point motors are another consideration when fitting to a layout. If the track is close to the outside framing of the baseboard, can you comfortably reach the fixing holes with drill and screwdriver to attach the motor to the baseboards?

Size certainly matters and the reason why this comes to the fore now is that the motor types described next are generally larger in size than servos and solenoids. On the flip side, large stall motors are among the most durable and reliable.

Stall motors

Stall motor point machines, such as

DCC Concepts ‘Cobalt’ and Circuitron ‘Tortoise’, are far from being new technology. Nonetheless, they have a reputation for reliability and ruggedness.

Also known as slow-motion point machines, they are powered with a large electric motor and gears which has a rotary action that moves the control wire from side to side about a fulcrum. The throw action is slow and will not place undue pressure on delicate point blades and stretcher bars.

Power is constantly applied to them and when at rest, they are stalled, with a small amount of current going through the motor. It is big enough not to burn out, but can buzz annoyingly when in the stalled position. The resulting torque has a major advantage by locking the points in place. This can be adjusted by the choice of control wire used to connect the motor to the turnout and the amount of throw. When using Peco turnouts, the centring spring can be removed because the torque does the point locking for you.

Stall motor turnouts generally come with built-in switches which are independent of the power supply for the motor. They have many uses such as polarity change switch for the crossing vee, indicator LEDs, signalling and other logic-based electronics, such as route setting.

They sound great except they are not suitable for a shallow shelf layout or one with shallow frames. The size is what makes them mechanically reliable, yet also is their Achilles heel.

For example, the DCC Concepts

standard ‘Cobalt’ motor measures 67mm deep from the mounting flange to the connector block. Its mounting footprint is 68mm by 48mm including the mounting flanges.

The ‘Tortoise’ is quite a bit larger at 82mm in depth including the mounting plate at the top. The mounting footprint is 46mm by 50mm. The front of the motor has a fulcrum or pivot plate which adds to the bulk of the motor. The baseboard frame depth would have to be 100mm to protect both motor and the wiring soldered to the connectors at the base of the motor.

IN FAVOUR

■ Rugged construction.

■ Slow throw action.

■ Simple wiring required to operate them.

■ Low current consumption, ideal for DCC control.

■ Usually have internal switches for accessories.

■ Simple to mount under the layout.

■ Positive latching effect through the control wire.

■ Built-in DCC versions are available.

POINTS AGAINST

■ Expensive.

■ Bulky, with large mounting footprint.

■ Awkward to mount close to baseboard framing.

■ Hard to disguise when mounted on top of the baseboard.

■ Deep baseboard frames are needed.

■ The pivoted throw action makes extended rod control difficult to set up.

■ Wiring can become untidy with the connectors mounted at the base.

■ Stalled motors can make a buzzing sound.

Switched motors

Similar to stall motors in concept are switched motors. They are powered with an electric motor and gearing in the same manner as stall motors and the motion is slower than solenoids too. The action is usually side-to-side in the same manner as solenoid motors.

There is an important difference between them and stall motors and that is the drive engages a limit switch at the end of the travel which kills the power. Consequently, the drive motor does not take current when at rest and there is no buzzing sound. Furthermore, the motor and gears can be smaller, reducing the footprint of the device.

The problem with switched motors is the limited length of travel, and consequently throw distance, for the turnout. Whilst there is a little leeway depending on the control wire used, their small size does not leave much distance between motor and turnout for

the control wire to flex. Some motors have different gear settings for different lengths of throw to suit the gauge and scale of turnouts – check before buying!

Several types of switched motor have appeared on the market over the years, perhaps the most well known being the old Fulgurex design which is quite bulky and also with a reputation for being very noisy. The MTB motors are a relatively new type which have internal control switches and adjustable throw lengths. The basic model, the MP1, is powered with a 12 volt motor and gearing built in to a body measuring 17mm deep, 40mm in length and

42mm wide over the mounting flanges. It can be fitted above and below the baseboard.

Reliability of the control switch and wear of the operating cam is a consideration in the long term. Simplicity is where stall motors have an advantage over switched motors against physical size. Where layouts with shallow frames and shelf layout designs are concerned, a small motorised point machine such as the MTB MP1 makes sense.

IN FAVOUR

■ Generally compact, making them useful for tight mounting situations.

■ Motor and gears provides a slow action.

■ The power supply can be stepped down using resistors.

■ Internal accessory switches are usually installed.

■ Suitable for mounting above and below the baseboard top.

■ Low current consumption.

■ No stall buzzing sound from the motor.

■ Can be run on AC and DC power.

POINTS AGAINST

■ The smaller size could mean less durability in the long term.

■ Fixed throw travel distances.

■ Motors can be noisy depending on the type.

■ Limiting switches can fail over time.

■ Difficult to mount precisely due to the limit on throw distances.

Mix and match

The reality is that the choice of motor won’t be restricted to one type. A yard

or siding might suit manual throws, whilst other areas of a layout may suit large stall motors. The choice is a matter of horses for courses, although standardisation is desirable for ease of maintenance and setting up control panels and where they are located.

Which one is best?

Deciding upon a motor based on ‘which one is best’ is not always easy, but in summary, consider the following factors:

■ Size of the point motor casing and depth of the layout frames.

■ Cost per motor.

■ Complexity of wiring and control panel switches.

■ Analogue or DCC control.

■ What type of turnouts you are planning to use.

■ Ease of mounting in hard to reach places.

■ Will the motor have the strength to throw your chosen turnouts?

■ The type of control panel and location of them around the layout.

■ Will route setting be a feature of your layout control?

↑ Slow motion stall motors are usually considered to be the best choice for hand-built turnouts. The slow switching action and long control wire pivoted about a fulcrum provides a smooth, gentle throw that does not put stress on soldered point stretcher bars. If a switched motor is used, the throw setting would have to be about 3mm to suit this design of turnout.

↑ Circuitron ‘Tortoise’ slow motion stall motors (shown with a decoder) have a reputation for being indestructible in normal use. However, they are large and relatively expensive, with an awkwardly located edge connector strip.

↑ Slow motion stall motors are among the most reliable machines for turnout control and can be easily powered with accessory decoders. A DCC Concepts Cobalt with decoder is shown.

Stall motors like the Tortoise have a rotary action where the wire moves from side to side around a fulcrum. This, combined with the stall action, is a good point lock system but makes extensions and control of more than one turnout awkward without special accessories.

Large stall motors are hard to disguise when mounted on top of the baseboard in locations with insufficient room on the underside. Note the simple extension rod connection motor to the turnout.

‘N’ gauge turnouts are naturally shorter, allowing less room under the baseboards for mounting large point motors. The point centring spring of Peco turnouts as used on this layout may be removed to make the throw action smoother.

Whilst the DCC Concepts stepper motor system is small and quiet, it needs to be set up carefully to match the desired turnout throw and a control board is needed for operation. Its use was described in the March 2019 issue of Rail Express Modeller.

There are two micro-switches in the MP1 switched motor, one of which is the control switch and the other for accessories. Note the drive shaft cams which make contact with the micro-switch buttons.

The throw limit of the MTB motor design can be changed by moving a cam spigot to different positions. Some trial and error might be needed to set them up properly for a given gauge and turnout type.

An example of a slow motion switched motor which has an internal kill switch that shuts power off when the machine has reached the end of travel. This is the MTB MP1 which has a very small footprint.

A large motor and rugged gearing is what makes stall devices so durable.